This invention relates generally to a leak detection apparatus and method for the detection and location of leaks in underground or underwater storage containments such as fuel and hazards material storage tanks, under dispenser containment (UDC), vaults, and sumps, and will be described in connection with such utility, although other utilities are contemplated.
It is standard in the oil industry to employ pressure tests, various types of still gauging, or liquid level measurements or to perform measurements of hydrocarbons in the subsurface to determine if a containment is leaking. Each of these conventional methods suffers significant practical shortcomings. Known pressure tests are known to be insensitive and thus are not reliable. The still gauging methods require the tank to be filled with product to a point above ground where changes in liquid level can be observed in a small diameter tube, all the while monitoring for the product temperature to take into account thermal expansion or shrinkage effects. The major drawbacks to this method are inconvenience due to disruption of tank service for about twelve hours and the expense for testing and for the purchase of sufficient product to fill a potentially leaking tank.
Testing for hydrocarbons in the subsurface is known to be highly unreliable due partially to the fact that surface spills create relatively high subsurface product vapor concentrations. Thus vapor detection for leaks seldom is considered as reliable, let alone conclusive.
Once the presence or existence of a leak has been confirmed, none of the know leak detection methods can determine the exact location of the leak. Traditional leak detection methods requires the dangerous time consuming and expensive process of excavating the entire area around the containment. Subsurface soil or soil vapor samples can be taken around the containment to help determine a leak location but old spills and leaks will confuse the operator of the region the leak could possibly be located but even in the best conditions the exact location of the leak cannot be determined.
The foregoing discussion of the prior art derives primarily from U.S. Pat. No. 4,725,551 in which there is described a method and apparatus for detection and location of leaks in subsurface fluid storage tanks by mixing a quantity of a tracer with the fluid in the tank, providing at least one subsurface vapor or air inlet sampling pipe in the backfill or vicinity of the tank, providing at least one positive pressure vapor pipe in the backfill or adjacent vicinity of the tank, and drawing air from the positive pressure pipe which is flowed past the tank into the sampling pipe, and analyzing the air drawn into the sampling pipes for the presence of the tracer, indicating the detection of a leak in the tank.
Other prior art patents describing the various other systems for monitoring for leaks in underground storage tanks include U.S. Pat. Nos. 4,709,577; 4,725,551; 5,046,353 and 5,048,324. All of these prior art systems are cumbersome, and do not provide easy and reliable methods for testing and pinpointing the location of a leak in a tank.
It is an object of the present invention to provide an improved leak detection apparatus and method for use in conjunction with underground and underwater container systems.
It is a further object of the present invention to provide a leak detection apparatus and method for detecting fluid leaks from subsurface and underwater liquid storage tanks.
A still further object of the present invention is to provide an improved leak detection apparatus and method for rapidly locating even small leaks in buried and underwater fuel storage containments and tanks.
Yet another object of the present invention is to provide a leak detection system and apparatus for use in conjunction with underground and underwater liquid storage tanks where a leak is suspected.
Still another object of the present invention is to provide a leak detection method and apparatus to use in conjunction with buried fuel tanks which can be implemented in new or existing service stations without requiring tank removal.